2025 Nobel Prize in Medicine Awarded to Trio for Immune System Breakthrough
On October 6, 2025, the Nobel Assembly at the Karolinska Institute announced that the Nobel Prize in Medicine or Physiology would be awarded to Mary E. Brunkow, Fred Ramsdell, and Shimon Sakaguchi. They were honored “for their discoveries concerning peripheral immune tolerance.” (NobelPress)
The prize recognizes a fundamental advance: how the body prevents the immune system from attacking its own healthy tissues, a mechanism essential for preventing autoimmune diseases. Their work has reshaped scientific understanding of regulatory T cells and how immune balance is preserved. (NobelPopular)
What Their Discovery Means
In the human body, the immune system must discriminate between harmful invaders (viruses, bacteria) and the body’s own cells. If this discrimination fails, the system may turn on healthy tissue, leading to autoimmune disorders.
Before this prize, much of immunology focused on central tolerance—the elimination of self-reactive immune cells in the thymus. But Brunkow, Ramsdell, and Sakaguchi illuminated another layer: peripheral tolerance, operating outside the thymus, where regulatory T cells (often called T-regs) actively suppress autoimmune responses. (NobelPopular)
- Shimon Sakaguchi made the first key step. In 1995, he identified a class of T cells that prevent immune overreaction.
- Mary Brunkow and Fred Ramsdell, in 2001, uncovered the gene Foxp3, mutations of which cause severe autoimmune disease in mice and humans.
- Later work demonstrated how Foxp3 is required for T-regs’ development and function. Their collective discoveries explain why a perfectly functioning immune system doesn’t always attack itself—even though many molecular patterns of invaders overlap with the body’s own molecules. (NobelPress)
Because of these insights, the medical community now explores therapeutic manipulation of regulatory T cells in areas like autoimmune diseases (e.g. Type 1 diabetes, rheumatoid arthritis), cancer immunotherapy, and transplantation tolerance. (ScientificAmerican)
Unexpected Delays in Contacting a Laureate
In an unusual twist, the Nobel committee was unable to immediately reach Fred Ramsdell to inform him of the prize. He was reportedly off-grid hiking in the wilderness, with no cell reception. His lab and the committee confirmed that his phone was likely in airplane mode or disconnected. (TheGuardian)
When news did reach him, it came in a surprising way: reportedly, his wife shouted while hiking, causing Ramsdell to think she saw a bear—then he learned it was the notification of the Nobel. (Reuters)
This unusual communication delay echoes past Nobel announcements where laureates were temporarily unreachable, but it underscores the security and logistic complexities built into the Nobel notification system. (TheGuardian)
Prize Announcement Schedule
The Nobel Prize announcements run annually over a dedicated week in October. For 2025:
- Medicine is announced first (October 6). (NobelAnnouncementSchedule)
- Physics, Chemistry, Literature, Peace, and Economics follow each in subsequent days.
All announcements are broadcast live via Nobel Prize digital channels. (NobelAnnouncementSchedule)
Why This Noble Prize Matters
This year’s award is more than academic. The work of Brunkow, Ramsdell, and Sakaguchi addresses one of immunology’s central puzzles: how our bodies avoid self-destruction even as they wage war on disease. Their findings not only fill a critical gap in basic science but also pave the way for new medical interventions.
Autoimmune diseases currently affect millions worldwide; therapies targeting the regulation of immune tolerance could revolutionize treatments. Moreover, in the context of cancer, suppressing or tweaking immune tolerance mechanisms may improve therapies that liberate the immune system against tumors.
Their discoveries also provide a unifying framework for transplant rejection, allergies, and chronic inflammation, giving researchers a more precise language and set of tools to tackle these challenges.